This invention is related to a process for the the application of two component polyurethane coatings and in particular to the prevention or substantial reduction of gelation in the process.
Two component polyurethane coatings are well known in the art as shown in Vasta U.S. Pat. No. 3,558,564 issued Jan. 26, 1971 and Miller U.S. Pat. No. 4,020,216 issued Apr. 26, 1977. However, there continues to be problem with formation of gel particles in equipment when streams of the two components i.e., of polyol and isocyanate are mixed before application. In a typical paint spray application line, a stream of polyol and a stream of isocyanate are mixed in an in-line mixer just before application. Under ideal conditions this mixed stream flows promptly and cleanly through the paint spray application equipment before any reaction occurs between the polyol and isocyanate. However, any stoppage of application of the paint as often occurs or a breakdown of the equipment results in the formation of soft and hard gel particles in the application equipment.
Most application equipment has small static or dead areas where small gel particles form. Under the worst conditions, complete gelation of the paint can occur which would require extensive down time for cleaning of the equipment or replacement of parts of the equipment. At the least, small gel particles interfere with the atomization of the paint, clog filters or show in the resulting finish as defects in the finish.
There is a need for an improvement in the application of two component polyurethanes that would eliminate or substantially eliminate formation of gel particles.